1. Field of the Invention
This invention relates to lined pipe and more particularly to flanges for the inner lining of a lined pipe.
2. Prior Art
In the prior art there exists several methods for forming a flange for the inner lining of a lined pipe and each of such methods has certain advantages and disadvantages. The earliest method for forming a flange for an inner lining of the lined pipe consisted of forming the flange on the end of the lining when the lining was provided within the outer pipe of the lined pipe. This method is disadvantageous for many reasons. The first reason is that this method requires expensive machinery to form the flange on the end of the inner lining. Another disadvantage is that lined pipe formed with flanges in this manner can not be cut to specific lengths at the place of installation because to do so would cut off the flange.
To overcome the above disadvantages, a method for providing a flange for inner lining has been developed. This method includes the steps of cutting the lined pipe such that a portion of the lining projects out of the lined pipe and the lining itself is flanged back utilizing heat and pressure. Such methods are described in U.S. Pat. Nos. 3,335,484; 3,383,750; 3,390,442 and 3,461,505. This method can be used at the point of installation to provide a flange for the inner lining when the pipe is cut to specific lengths. But again this method has a disadvantage in that the lining in the region of the flange tends to fail with time. To overcome this disadvantage, another method has been developed which simply requires a gasket which forms the flange for mating pipes at the point where the two lined pipes are joined together. This method also allows for changes in the length of the lined pipe at the point of installation but has a particular disadvantage in that the gasket is easily damaged and must be installed with great care to insure that there is no leak.